vibration damper for damping fluid vibrations in a hydraulic system

ABSTRACT

The invention relates to a vibration damper for damping fluid vibrations in a hydraulic system, especially in a hydraulic control circuit for a motor vehicle gear box with an elastically deformable damper element ( 31 ), According to the invention, the vibration damper is provided with a separate sealing element ( 32 ) which guarantees the functioning of the hydraulic system in the event of a breakdown e.g. the damper element ( 31 ) bursting.

FIELD OF THE INVENTION

The invention concerns a vibration damper for the damping of fluidvibrations in a hydraulic system, especially in a hydraulic controlcircuit for a motor vehicle transmission wherein said vibration damperpossesses an elastic, deformable damping element.

BACKGROUND OF THE INVENTION

Vibration dampers of the above kind are installed in motor vehicletransmissions for the adjustment of the control pressure in the valvesas well as for the damping of vibratory oscillations in the fluidpressure medium. The damping elements are customarily made of anelastomer and thus are elastically deformable upon changes in load fromdifferent fluid pressures.

DE 195 24 921 A1, for instance, discloses such a vibration damper. Thispatent teaches of a vibration damper with a membrane, which isconstructed from an elastomer as a component in the form of a hollowcylinder. The failure of an elastomer membrane of this nature, forinstance by leakage because of bursting, leads, generally, to thefailure of the entire vibration damper. Because of this, the controllingpressure in the hydraulic system drops and the transmission is no longercontrollable. This leads to contingent damage to the transmission andcan finally result in the immobilization of the vehicle.

SUMMARY OF THE INVENTION

Thus, the purpose of the invention is to prevent a pressure loss at avibration damper upon failure of the damping element, so that atransmission failure with contingent immobilization of the vehicle isavoided.

This purpose is achieved, by a generic vibration damper, wherein asealing element is provided, which secures the function of the hydraulicsystem upon a failure of the damping element, for instance by leakagebecause of bursting. In this way, advantageously, a free fluidthrough-flow action is blocked, so that upon a failure of the dampingelement a pressure drop in the hydraulic control circuit is prevented.Even in the case of a defective damping element, the function of thetransmission remains essentially in force and an immobilization of thevehicle is avoided. If a possible difficulty in shifting qualityappears, which can occur from a burst damping element, then as a matterof course, the damping element is to be replaced.

A preferred embodiment of the invention offers the proposition, that thedamping element be placed in a recess of a housing, further, that thishousing possess an opening, in particular, an orifice to serve as theinlet of a pressurized fluid to the damping element. In addition, apressure equalization port in said housing is provided. With thisarrangement, advantageously, the sealing element, in case of failure ofthe elastically deformable damping element, closes the pressurecompensation opening. Thus, a solution is brought about, by which,during normal operation of the vibration damper, when the dampingelement exhibits no leakage, the vibrations of the fluid pressure aredamped by elastic deformation and the pressure compensation opening isheld open, so that a pressure equalization in two chambers before andafter the said sealing element takes place and that, by means of theextenuation of the damping element, volumes of air compressed in theforward chamber escape through the pressure equalizing opening. As thishappens, the chambers are defined before and after the sealing element,regarded in the direction of the flow from the throttle valve to thepressure equalizing opening.

In a further development, the proposal is made that the sealing elementand/or the damping element be movably placed in the recess. In this way,several advantageous possibilities arise in the formulation of the twoessential elements of the vibration damper.

In one advantageous design of the invention, it is proposed, that thepressure side orifice and the pressure equalization port be respectivelyplaced in essentially oppositely situated end locations of the recessand that the sealing element be provided near to the orifice and thedamping element be placed near to the pressure equalization port.

A particularly advantageous design of the vibration damper is found,wherein the sealing element is constructed as essentially a cylindricalpiston, and the recess in the housing is bored as a piston boring inwhich the said piston is guided to be axially displaceable. In thisarrangement, the cylindrical outer shell of the piston sealinglycontacts the cylindrical inner wall of the piston boring, so that thetwo fluid chambers, located forward and after the two ends of thepiston, are separated, one from the other.

In another development of the invention, the piston, on at least oneend, is provided with a conically shaped boring, which serves to centerthe damping element.

The damping element itself is constructed as a sphere, wherein thediameter of the sphere is less than the diameter of the piston or thepiston boring. In this way, the sphere is advantageously centered withinsaid conically shaped boring at one end of the piston.

The piston, as well as the housing which encloses it, is comprised ofmaterials with essentially equal heat expansion coefficients, so that byany possible heating of the vibration damper, the sealing functionbetween the piston and the piston boring is advantageously assured.

The piston is advantageously made of a plastic, especially Ryton© or asimilar construction material. The housing can be fabricated of aluminumor equal material.

The damping element, on the other hand, is made of an elastomer,especially nitrile butadiene rubber (NBR) or a similar raw material, andpossesses accordingly, an advantageous damping characteristic.

In a further embodiment of the invention, the proposal is to place thedamping element close to the orifice and the sealing element close tothe pressure equalization port of the recess. In this way,advantageously, an arrangement is undertaken opposite to that of thepreviously described design with an reversed positioning of the twoelements.

It is advantageous, if the damping element is designed as an essentiallyhollow cylindrical and elastically deformable component, and providedwith one essentially open and one essentially closed end piece for theacceptance of the fluid in the internal chamber of the damping element.

The sealing element is essentially shaped as a circular plate, anannular ring, a plate, a cone, as a cup, or is a similarly shapedcomponent and is placed preferably on the outside of the closed end ofthe damping element.

By the construction of the sealing element in a conical or cup shapedform, the said element opens favorably in the direction of the open endof the damping element and thus toward the orifice, so that in a case ofthe bursting of the damper element, and an escape of the pressurizedfluid out of the damper element, an effective sealing function isaccomplished by the sealing element.

In an additional development, the sealing element exhibits on its outerradial rim, a lip seal running essentially around its circumference.During normal operation of the damping element, this lip seal liesnearly completely against the inner wall of the recess, thereby dividingthe recess into chambers, one forward and one after the said lip seal,as seen in the direction of the flow.

In a further design of the sealing element, the lip seal is shapedelliptically, so that it forms, within the predominately cylindricalconstruction of the inner wall of the recess, escape penetrations ofspecifically designed opening between the lip seal and the said innerwall.

In yet another, embodiment of the sealing element, especially to bepreferred, the sealing element is essentially annular in shape and thediameter of the lip seal is, when not installed, greater than that ofthe inside diameter of the essentially cylindrical recess. By thismeans, assurance is given, that the lip seal, when installed, will laystressed against the said inner wall of the recess.

So that a pressure exchange of the two chambers of the recess, beforeand after the lip seal, can be brought about, this seal is provided withat least one through opening.

The said through opening is advantageously so designed and theelasticity of the lip seal is selected in such a manner, that in thecase of failure, for instance by bursting of the damping element, bymeans of which failure, due to the unilateral force of the existingfluid pressure in the chamber forward of the lip seal, a circumferentialseal is formed by the said lip seal against the inner wall of the recesswhich encompasses the damper.

In this way, a simple solution is proposed, which assures, that afterthe bursting of the damper element, the lip seal is reliably pressedagainst the inner wall of the recess, and thereby closes the pressureequalization port. The efficiency of the damping is indeed lost to aconsiderable degree, however, the control pressure in the vibrationdamper does not lead directly to loss of function by the transmission.

In a further preferred embodiment of the invention, the sealing elementis designed as an elastic, essentially circular, annular plate and isconnected coaxially with the damping element.

When this is done, the sealing element is shaped in such a way, that itdoes not directly touch the inner wall of the recess during the normaloperation of the vibration damper, so that the chamber forward of thesealing element communicates with a chamber behind the sealing element.With this arrangement, under normal operational conditions, a pressureequalization is effected between the two chambers before and after thesealing element with the result that upon the expansion of the dampingelement, the volumes of air pressed out of the forward chamberadvantageously escape through the said pressure equalization port to theafter chamber.

The sealing element itself, as well as the connecting of the sealingelement onto the damping element is carried out in such a manner, thatthe sealing element, in case of failure, closes off the pressureequalization port. This can be effected, for instance, since thecentralized and essentially neck shaped connection piece between thedamping element and the sealing element is so elongated by the fluidpressure on the one side of the sealing element, that the said sealingelement is pressed against a sealing seat of the recess.

Advantageously, the sealing element is designed to be flexible, so thatit is elastically deformed in its radial, outward area by the fluidpressure on one side and is thus pressed against an annular sealing seatof the recess, thus closing the pressure equalization port.

The sealing element as well as the damping element are constructed asseparate components. Thus, the exchange of a single defective componentas well as the separate fabrication of the two components in differentconstructive materials becomes simple to do, so that each component canbe made as a sealing element or a damper element from the mostappropriate materials.

However, as an alternative, the sealing element and the damping elementcan be made in one-piece construction, for instance, from an elastomer.Such a one-piece proposal offers an especially economical production ofthe sealing element and the damping element.

BRIEF DESCRIPTION OF THE DRAWING(S)

Further goals, features, advantages and application possibilities of theinvention arise in the following explanation of an embodiment, which ispresented in more detail with the aid of the drawings. In thisexplanation, all described and/or illustratively presented features,form the object of the invention, of themselves alone, or in optional,reasonable combination, independently of their summations in the claimsand their inter-claim relations. There is shown in:

FIG. 1 a vibration damper with an essentially hollow cylinder shapeddamping element in longitudinal section,

FIG. 2 a vibration damper conforming to FIG. 1 in cross-section throughline 2—2 of said figure,

FIG. 3 a vibration damper similar to the presentation of FIG. 1, howeveralternative in that a plate shaped sealing element is presented inlongitudinal section, and

FIG. 4 a vibration damper in an alternative design, with a sealingpiston as well as a spherical shaped damping element.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a vibration damper 1 (FIGS. 1, 2) comprises ingeneral a damper element 3 with a sealing element 7 which is insertedinto a recess 11 of a housing 9, for instance, of a motor vehicletransmission. The damping element 3 is formed by an essentially hollow,cylindrical midsection 5, which, on its open end is provided with anannular flange projection 4 which is fixed in place within the housing 9by a cover plate 10. The opposite end the damping element 3 exhibits anessentially cup shaped, closed bottom 6 and thus defines a somewhatcylindrical inner chamber 8 of the damping element 3. On the outer sideof the bottom 6 is provided a generally cup shaped sealing element 7,which is centrally connected with the damping element 3.

The damper element 3 is inserted into the recess 11 at a radial spatialinterval from the inner wall thereof. The sealing element 7, especiallywith its radially disposed outer lip seal lies against the inner wall ofthe recess 11. In the said cover plate 10 is provided an opening, forexample, this being in the form of a restrictive orifice 12 , in orderto bring into the inner chamber 8 of the damping element 3 thepressurized fluid at pressure p. On the opposite end of the recess 11,as seen in the direction of flow, is provided a pressure equalizationport 13, this being for instance in the form of a boring. During normaloperation of the damper element 3 and under an increase in the pressureof the fluid in the inner chamber 8 of the damper element 3, theelastically deformable midsection 5 of the damping element 3 extendsitself outwardly, thus reducing the volume of the forward air chamber 15above the sealing element 7. The volumes so expressed out of thisforward chamber 15 are forced through the two radially outer escapeopenings 14 in the lip seal 7 into the after chamber 16 underneath thesaid lip seal. By this action, a pressure equalization between the twochambers 15, 16 is effected, whereby the after chamber 16 communicateswith the atmospheric ambience. The said escape openings 14 are, as anexample, situated diametrically opposed to one another in the sealingelement 7.

If, now, in a case of failure, for instance the wall of the midsection 5of the damping element 3 tears or bursts, and the pressurized fluiddischarges into the forward chamber 15 above the sealing element 7,then, through the two, small dimensioned escape openings, 14 of the lipseal, a turbulent flow arises, which results in a compression of the lipseal against the inner wall of the recess 11. First, the damping actionis largely lost by this flow blocking action, however, second, thecontrol pressure is retained in the inner chamber 8 of the dampingelement 3, and thus also in the therewith connected hydraulic controlcircuit, so that a transmission functional failure is advantageouslyavoided.

In an alternative construction, (FIG. 3) the damping element 17 with itsprojecting flange 18, along with the mid-section 19 and the bottom 20follow essentially the presentation in FIG. 1. This damping element 17is inserted into a recess 25 of a housing 24, whereby the recess 25 isprovided on one of its ends with a cover plate 26 having an orifice 27.On the opposite end of said recess 25, is a pressure equalizing port 28.

The principal difference in the design according to FIG. 3 from thedesign depicted in FIG. 1 lies therein, that the sealing element 21 ismade as a generally circular disk shaped plate which, by means of acentrally located neck 22 is affixed to the bottom 20 of the dampingelement 17. The sealing element 21 is, in this construction, sodesigned, that, when inserted in recess 25, it possesses acircumferentially running opening 29 between the sealing element 21 andthe inner wall of the recess 25, which remains open during normaloperation of the damping element 17, i.e. when there is no leakageoccurring from the mid-sectiorn 19. In this way, an equalization ofpressure between forward chamber 30 above the sealing element 21 and thepressure equalization port 28 is established. In the case of failure,for instance by the bursting of the mid-section 19 of the dampingelement 17, a pressure increase occurs in forward chamber 30, wherebythe radial, outward projecting annular area of the sealing element 21 issealingly compressed against a matching annular, seating surface of therecess 25 of the housing 24. By this means, the inner chamber 23 of thedamping element 17, that is to say, also the chamber 30, is thus closedoff against the ambient atmosphere. The damping action of the dampingelement 17 is indeed lost, however, the controlling pressure is retainedin the hydraulic control circuit, whereby a contingent failure of thetransmission is prevented.

In a further alternative construction (FIG. 4) the proposal is, that thesealing element is to be designed as essentially a cylindrical piston32, which sealingly makes contact with the inner wall of the pistonboring 41 in the housing 34. The piston 32 is loaded by pressure on theone side by the orifice 36 in the housing cover plate 35, so, that thepiston moves itself within the recess 37 in the direction of thepressure equalization port 40, wherein the pressure equalization port 40is located on the end of the recess 37 opposite from the orifice 36.

In the after chamber 39, which, seen in the direction of flow, is foundbehind the piston 32, is placed an elastic deformable sphere. This iscentered by a conical boring 33 on one end of the piston 32. By means ofthe pressure application of the chamber 38, which, as seen in directionof flow, is placed on the front of the piston 32, the damping element 31is compressed, dependent upon the increasing fluid pressure. The airvolumes pressed out of the chamber 39, can escape through the pressureequalization port 40 from the housing 34.

The piston 32, as well as the housing 34 which encompasses it, areadvantageously made of raw materials with closely equal heat expansioncoefficients. That is to say, that the piston is made of a plastic, inparticular Ryton © and the housing is constructed of aluminum, so thatupon a heating of the vibration damper, the piston 32 remains in asealing contact against the piston boring 41. The spherical dampingelement 31 is advantageously fabricated from an elastomeric rawmaterial, especially from NBR. In a possible case of failure of thedamping element, wherein, for example, the elastomer material cracks orbursts, then, first the damping action will be lost, second, however, bymeans of the piston 32 at any time a sealing function of the vibrationdamper is assured, so that here again, the control pressure in thehydraulic circuit can be maintained and a contingent transmissionfailure is avoided.

What is claimed is:
 1. A vibration damper for the damping of vibrationsof fluid in a hydraulic circuit, the vibration damper comprising: ahousing (34); a recess (11, 25, 37) formed in the housing; an opening(12, 27, 36) formed in the housing for allowing passage of pressurizedfluid therethrough from a hydraulic circuit, communicating with thevibration damper, into the recess (11, 25, 37) and passage from therecess (11, 25, 37) to the hydraulic circuit; a pressure equalizationport (13, 28, 40) formed in the housing and communicating with therecess (11, 25, 37); and a sealing element (32) and an elastomericelastically deformable damping element (31) located within recess (11,25, 37) between the opening and the pressure equalization port, thesealing element (32) having a centrally located boring which partiallyreceives and centers the damping element (31) within the recess (11, 25,37) and the pressure equalization port (13, 28, 40) is spaced from thesealing element (32) so that the pressure equalization port (13, 28, 40)is unobstructed by the sealing element (32) during normal operation;wherein, upon failure of the damping element, the sealing element closesthe pressure equalization port to assure continued functioning of thehydraulic circuit.
 2. The vibration damper in accordance with claim 1,wherein the opening for allowing passage of the pressurized fluid to afront face of the damping element (3, 17, 31) is an unobstructed orifice(12, 27, 36) and a front face of the sealing element (32) is spaced froman inwardly facing surface of the housing (34) so that the housing andthe sealing element (32) define an interior chamber (8, 23, 38)therebetween for accommodating the pressurized fluid.
 3. The vibrationdamper in accordance with claim 2, wherein at least one of the sealingelement (7, 21, 32) and the damping element (3, 17, 31) is movablylocated within the recess (11, 25, 37) and a central region of the frontface of the sealing element (7, 21, 32) is continuously spaced from theunobstructed orifice (12, 27, 36).
 4. The vibration damper in accordancewith claim 1, wherein the opening (12, 27, 36) for allowing passage ofthe pressurized fluid and the pressure equalization port (13, 28, 40)are located at opposite ends of the recess (11, 25, 37) and the sealingelement (32) is located adjacent and faces the opening (12, 27, 36) forallowing passage of the pressurized fluid and the damping element (31)is located adjacent the pressure equalization port (40).
 5. Thevibration damper in accordance with claim 1, wherein the sealing elementis a cylindrical piston (32) and the recess (37) is constructed as apiston boring (41) and the cylindrical piston (32) is axiallydisplaceably guided within the piston boring (41) and a cylindricalouter surface of the cylindrical piston (32) is in sealing contact withan inner wall of the piston boring (41).
 6. The vibration damper inaccordance with claim 5, wherein a surface of the damping element (31)which abuts against the housing (34) is generally spherical in shape. 7.The vibration damper in accordance with claim 5, wherein at least aportion of the damping element (31) which abuts with the housing (34) issolid and spherical in shape and the spherical portion of the dampingelement (31) has a diameter which is less than a diameter of the piston(32) and less than a diameter of the piston boring (41).
 8. Thevibration damper in accordance with claim 5, wherein the cylindricalpiston (32) and the housing (34) are manufacture from materials whichhave substantially equal coefficients of expansion.
 9. The vibrationdamper in accordance with claim 8 wherein cylindrical piston (32) ismanufacture from a plastic and the housing (34) is manufactured fromaluminum.
 10. The vibration damper in accordance with claim 1, whereinthe housing (34) is manufactured from aluminum.
 11. The vibration damperin accordance with claim 1, wherein the sealing element (32) and thedamping element (31) are two separate components.